An electric train runs by converting power taken in from an overhead line by a current collector with a power converter, and driving an electric motor with the converted power. When a disconnection between the power converter and the electric motor occurs, power can no longer be supplied to the electric motor, and the electric train loses traction. Also, when a single power converter supplies power to multiple electric motors, if the power converter continues to operate in a state in which a disconnection has occurred between the power converter and one of the electric motors, the voltage applied to the other electric motors rises, and there is a risk of electric motor failure due to overloading the other electric motors. Accordingly, it is necessary to detect disconnections occurring between a power converter and an electric motor.
In the drive control device disclosed in Patent Literature 1, the drive control device computes an average value of a three-phase current output to an electric motor, and when the difference between the average value and each of the phase currents exceeds a set value, the drive control device determines that a cable for supplying that phase current is disconnected. The power conversion device disclosed in Patent Literature 2 determines that a disconnection between a power converter and an electric motor has occurred when the variation in the output current of the power converter exceeds a set value, and additionally, the minimum value of the output current falls below a set value.
The electric train control device disclosed in Patent Literature 3 determines that a disconnection between a power converter and an electric motor has occurred when the variation in the torque of the electric motor exceeds a set value. The electric motor driving device disclosed in Patent Literature 4 determines whether or not a disconnection between an output circuit and an electric motor has occurred on the basis of each phase voltage output by the output circuit within a set time after activation. With the technology disclosed in Patent Literature 5, it is determined whether or not a disconnection between the arm of each phase and an electric motor has occurred on the basis of a middle point voltage of the arm of each phase of a power converter before the electric motor starts up.